Multistage nanoreactor catalyst and preparation and application thereof

ABSTRACT

The present disclosure discloses a multistage nanoreactor catalyst and preparation and application thereof, belonging to the technical field of synthesis gas conversion. The catalyst consists of a core of an iron-based Fischer-Tropsch catalyst, a transition layer of a porous oxide or porous carbon material, and a shell layer of a molecular sieve having an aromatization function. The molecular sieve of the shell layer can be further modified by a metal element or a non-metal element, and the outer surface of the molecular sieve is further modified by a silicon-oxygen compound to adjust the acidic site on the outer surface and the aperture of the molecular sieve, thereby inhibiting the formation of heavy aromatic hydrocarbons. According to the disclosure, the shell layer molecular sieve with a transition layer and a shell layer containing or not containing auxiliaries, and with or without surface modification can be prepared by the iron-based Fischer-Tropsch catalyst through multiple steps. The catalyst can be used for direct preparation of aromatic compounds, especially light aromatic compounds, from synthesis gas; the selectivity of light aromatic hydrocarbons in hydrocarbons can be 75% or above, and the content in the liquid phase product is not less than 95%; and the catalyst has good stability and good industrial application prospect.

TECHNICAL FIELD

The disclosure herein relates to a multistage nanoreactor catalyst andpreparation and application thereof, in particular to a multistagenanoreactor catalyst for directly preparing aromatic compounds fromsynthesis gas and preparation and application thereof, belonging to thetechnical field of synthesis gas conversion.

BACKGROUND

Aromatic compounds including benzene, toluene and xylene (BTX) areimportant chemical basic raw materials, mainly derived frompetroleum-based production processes, such as naphtha steam cracking forproducing ethylene and catalytic reforming or cracking for producinggasoline and diesel. With the light weight of olefin raw materials, thereduction of crude oil resources and the increasingly prominentenvironment issues, the acquisition of aromatic compounds from petroleumhas been challenged and unsustainable. Therefore, the non-petroleumroute to prepare aromatic hydrocarbons has received more and moreattention.

Based on China's energy structure of rich coal and poor petroleum, Chinahas been supporting the development of new technologies for producingvarious chemical products using coal and biomass as raw materials in thepast decade, from the perspective of energy strategy and safety, so asto reduce the dependence on petroleum. As the coal gasification processapproaches maturity, the direct preparation of aromatic hydrocarbonsfrom synthesis gas as an alternative technical route for producing BTXis of great significance for utilizing China's rich coal resources andrelieving the dependence on petroleum resources. The process does notrequire further preparation of aromatic hydrocarbons from synthesis gasthrough methanol or dimethyl ether as in an indirect process, so thatthe process is simplified, the operating cost is low, and the investmentis greatly reduced.

At present, the direct preparation of aromatic hydrocarbons fromsynthesis gas is mainly implemented by placing two catalysts having asynthesis gas conversion function and a dehydro-aromatization functionin a tandem double-bed reactor sequentially or placing the same into asingle-bed reactor in an inter-particle or intra-particle mixing manner.For example, the two-stage reactor used in Shanxi Coal Chemical Plant ofChina is respectively charged with two types of catalysts, which canconvert the synthesis gas into aromatic hydrocarbons through dimethylether. In addition, the Guan Naijia research group in Nankai Universityreported that the Fischer-Tropsch synthesis (FTS) catalyst Fe/MnO wasphysically mixed with the Ga/HZSM-5 catalyst, and the aromatichydrocarbon selectivity was close to 50% under 1.1 MPa at 270° C.

However, direct composite catalysts have certain limitations for thedirect preparation of aromatic hydrocarbons from synthesis gas. Forexample, intermediates that are susceptible to aromatization, such asC2˜C5, still need to undergo several times of diffusion to enter theactive centers of the aromatization catalysts for activation andreaction. At the same time, these intermediates have the opportunity toescape. Meanwhile, after CO undergoes a CO conversion catalyst, the COoften cannot continue to activate and react on a second catalyst.Moreover, the physical mixing easily causes non-uniform distribution oftwo active site concentrations in the reaction system, which will affectthe aromatization reaction of the intermediates to varying degrees. Inthe presence of these problems, the ultimate aromatic hydrocarbonselectivity and yield are generally not high, especially light aromatichydrocarbons such as benzene, toluene and xylene.

SUMMARY

In view of the problems in the conventional catalysts, the presentdisclosure relates to a multistage nanoreactor catalyst capable ofrealizing one-step high-selectivity preparation of aromatic compoundsfrom synthesis gas, as well as preparation and application thereof inreactions of preparation of aromatic compounds from synthesis gas. Thedesigned catalyst has high aromatic hydrocarbon selectivity, especiallyfor light aromatic hydrocarbons, and is expected to be appliedindustrially.

The catalyst according to the present disclosure is a multistagenanoreactor catalyst for directly preparing aromatic compounds fromsynthesis gas, and the multistage nanoreactor catalyst is composed of astructure of a core layer, a shell layer and a core-shell transitionlayer (as shown in FIG. 1). The core layer is an iron-based catalysthaving Fischer-Tropsch activity for activating CO, CO₂ and H₂ andforming a main product of olefin, the weight of the core layer being0.1% to 80% of the total weight of the catalyst; the shell layer is amolecular sieve for forming an aromatic hydrocarbon product, the weightof the shell layer being 0.1% to 80% of the total weight of thecatalyst; and the core-shell transition layer is a porous oxide orporous carbon material, the weight of the transition layer being 0.01%to 35% of the total weight of the catalyst.

In one embodiment of the present disclosure, the iron-based catalysthaving Fischer-Tropsch activity may be a supported or unsupportedcatalyst, and contains or does not contain additives.

In one embodiment of the present disclosure, the molecular sieve is oneor a mixture of two or more of ZSM-5, MCM-22, MCM-49, and SAPO-34zeolite molecular sieve materials.

In one embodiment of the present disclosure, the molecular sieve may ormay not contain additives.

In one embodiment of the present disclosure, the outer surface of themolecular sieve has or does not have a silicon-oxygen compound.

In one embodiment of the present disclosure, the silica-alumina ratio ofthe zeolite molecular sieve is preferably 10 to 500; when additives areadded, the additives are one or more of P, V, Cr, Mn, Fe, Co, Cu, Zn,Ga, Ge, Zr, Mo, Ru, Pd, Ag, W and Re, and the weight of the additives is0.01% to 35% of the weight of the shell layer based on atoms; and theweight of the silicon-oxygen compound on the outer surface of themolecular sieve is 0.01% to 20% of the weight of the shell layer.

In one embodiment of the present disclosure, the porous oxide of thetransition layer is one or more of silicon oxide, aluminum oxide,zirconium oxide, magnesium oxide, zinc oxide, titanium oxide and calciumoxide, and the thickness of the transition layer is 0.1 to 1000 nm,preferably 0.5 to 100 nm.

A preparation method of the catalyst according to the present disclosurecomprises the following steps:

step 1, admixing a prepared iron-based catalyst into an organic solventcontaining a transition layer oxide precursor, continuously stirring for0 to 24 h, then performing rotary evaporation to remove the solvent anddrying at 30 to 250° C. for 0 to 24 h to obtain a sample;

step 2, admixing the sample prepared in step 1 into an alkaline solutioncontaining a template, a silicon source and an aluminum source, andstirring for 0 to 24 h, wherein the weight ratio of the sample, thetemplate, the silicon source, the aluminum source, alkali and water is(0.5-50):(0.05-1):1:(0.01-1):(0.001-0.5):(10-500); then charging into ahydrothermal kettle, sealing, heating to 110 to 300° C., andhydrothermally crystallizing for 5 to 120 h; filtering a solid productafter crystallization and cooling, washing till the pH value of washingliquid is 4 to 11, then drying at 30 to 200° C. for 0 to 24 h, andcalcining at 300 to 800° C. for 0 to 24 h to obtain a powder sample;

step 3, admixing the powder obtained in step 2 into a solutioncontaining a soluble salt of a metal element by an incipient wetnessimpregnation method or an ion exchange method or an excess impregnationmethod, the soluble salt being preferably one or more of nitrate,carbonate, acetate, sulfate, molybdate, tungstate and chloride; and

step 4, admixing the sample powder obtained in step 3 into an organicsolvent containing a silicon source, stirring, then removing the solventby rotary evaporation and drying at 30 to 250° C. for 0 to 24 h, andfinally calcining at 350 to 650° C. for 0 to 24 h, wherein the contentof the silicon source being 0.01 to 20%.

In one embodiment of the present disclosure, in step 1, the organicsolvent is one or more of ethanol, propanol, acetone, cyclohexane,n-hexane, n-heptane and n-pentane.

In one embodiment of the present disclosure, in step 2, the adoptedtemplate is one or more of tetrapropylammonium hydroxide, n-propylamine,isopropylamine, hexamethyleneimine, triethylamine and tetraethylammoniumhydroxide; the silicon source is one or more of silicon oxide, sodiumsilicate, propyl orthosilicate, hexamethyldisiloxane, ethylorthosilicate and isopropyl orthosilicate; the aluminum source is one ormore of alumina, aluminum isopropoxide trihydrate, sodium aluminate,aluminum sulfate, boehmite and gibbsite; and the alkali is one or moreof sodium hydroxide, potassium hydroxide, potassium carbonate, sodiumcarbonate, sodium bicarbonate, potassium bicarbonate and sodium acetate.

The present disclosure also provides a method of applying the catalystto direct preparation of aromatic compounds from synthesis gas.

The catalyst needs to be pre-reduced before use: the pretreatmentreducing atmosphere is one or more of hydrogen, carbon monoxide,methane, ethane and ethylene gas; the pretreatment temperature is 150 to600° C., preferably 280 to 450° C.; the pretreatment pressure is 0.1 to3 MPa, preferably 0.1 to 1 MPa; the volume space velocity of thepretreatment gas is 1000 to 50000 h⁻¹, preferably 1500 to 20000 h⁻¹; andthe pretreatment time is 1 to 24 h, preferably 1 to 6 h.

The reaction condition suitable for the catalyst is: the reaction gascontains a gas mixture of one or two of carbon monoxide and carbondioxide, and hydrogen; the volume fraction of hydrogen is 5% to 85%; thereaction temperature is 150 to 600° C., preferably 250 to 450° C.; thereaction pressure is 0.1 to 5 MPa, preferably 0.2 to 2.5 MPa; and thereaction space velocity is 500 to 50000 h⁻¹, preferably 1500 to 20000h⁻¹.

The reaction using the catalyst of the present disclosure can be carriedout in a fixed bed, fluidized bed or slurry bed reactor, preferably afixed bed or fluidized bed reactor.

The present disclosure has the following advantages:

(1) The multistage nanoreactor catalyst prepared in the presentdisclosure can effectively avoid the influence of the shell layermolecular sieve on the core layer catalyst, improve the conversion rateof CO and promote further conversion of the olefin. The catalystprepared in the present disclosure is suitable for the reactionprocesses for directly preparing aromatic hydrocarbons using coal-based,biomass-based and natural gas-based synthesis gas as raw materials,particularly for the reaction of preparing light aromatic compounds; theselectivity of light aromatic hydrocarbons in hydrocarbons is up to 75%or above, and the content in the liquid phase product is not less than95%.

(2) The multistage nanoreactor catalyst prepared in the presentdisclosure has relatively high aromatic hydrocarbon selectivity,especially the selectivity to light aromatic hydrocarbons, can betterinhibit heavy and polycyclic aromatic hydrocarbon such as naphthalene,and has relatively low methane selectivity.

(3) The catalyst has good stability and good industrial applicationprospect.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a schematic diagram showing the structure of a multistagenanoreactor catalyst in an embodiment of the present disclosure.

DETAILED DESCRIPTION Examples 1˜6: Preparation of Multistage NanoreactorCatalyst for Direct Conversion of Synthesis Gas to Aromatic Compounds

Product analysis: the products left from the reactor were condensed in acold trap, while the uncondensed components were analyzed on-line by agas chromatography with TCD and FID detectors. In detail, the unreactedCO, formed CO₂ and CH₄, and inert gas N₂ were separated by a packedcolumn of TDX-01 and detected by TCD, and the N₂ was used as internalstandard substance for calculation of CO conversion. C1-C5 hydrocarbonswere separated using an HP-PLOT/Al₂O₃ capillary column. The condensedhydrocarbons were collected after reaction and analyzed by another gaschromatography off-line which connected with an FID and a capillarycolumn of HP-1 or FFAP for further separation of para-, ortho- andmeta-xylene.

(1) The total CO conversion X_(CO) was calculated as:X _(CO)=((A _(CO) /A _(N) ₂ )_(in)−(A _(CO) /A _(N) ₂ )_(out))/(A _(CO)/A _(N) ₂ )_(in)×100

where (A_(CO)/A_(N) ₂ )_(in) and (A_(CO)/A_(N) ₂ )_(out) are the peakarea ratio of CO to N₂ at the inlet and outlet of reactor, respectively.

The selectivity of CO converted to CO₂ (S_(CO to CO) ₂ ) was calculatedas:S _(CO to CO) ₂ ={(A _(CO) ₂ /A _(N) ₂ )_(out) ×f _(CO) ₂ /((A _(CO) /A_(N) ₂ )_(in)−(A _(CO) /A _(N) ₂ )_(out) ×f _(CO)}×100

where (A_(CO) ₂ /A_(N) ₂ )_(out) is the peak area ratio of CO₂ to N₂.f_(CO) ₂ and f_(CO) are the correction factors of CO₂ and CO,respectively.

(3) The selectivity of CO converted to hydrocarbons (S_(CO to HC)) wascalculated as:S _(CO to HC)=100−S _(CO to CO) ₂

Definitely, the CO₂-free selectivities of CO converted to CH₄, C₂-C₆ ingas phase, and hydrocarbons in liquid phase, namely the CO₂-freehydrocarbon distribution, were calculated as:

a) The CO₂-free selectivity of CO converted to CH₄ was calculated as:S _(CO to CH) ₄ =(A _(CH) ₄ /A _(N) ₂ )_(out) ×f _(CH) ₄ /((A _(CO) /A_(N) ₂ )_(in)−(A _(CO) /A _(N) ₂ )_(out))×f _(CO))×100/S _(CO to HC)

Where S_(CO to CH) ₄ is the selectivity of CH₄. (A_(CH) ₄ /A_(N) ₂)_(out) is the on-line TCD peak area ratio of CH₄ to N₂. f_(CH) ₄ is thecorrection factor of CH₄.

b) The CO₂-free selectivities of CO converted to C₂-C₆ hydrocarbons ingas phase were calculated as:S _(CO to C) _(n) =A _(C) _(n) ^(FID1) ×f _(C) _(n) ^(FID1)/(A _(CH) ₄^(FID1) ×f _(CH) ₄ ^(FID1))×S _(CO to CH) ₄

Where A_(C) _(n) ^(FID1) and A_(CH) ₄ ^(FID1) are the on-line FID peakareas of C_(n) (n=2-6) and CH₄, respectively; f_(C) _(n) ^(FID1) andf_(CH) ₄ ^(FID1) are the correction factors of C_(n) (n=2-6) and CH₄ inon-line FID, respectively.

a) The CO₂-free selectivities of CO converted to total hydrocarbons inliquid phase were calculated as:S _(CO to C) _(liquid phase) =100−S _(CO to CH) ₄ −Σ_(n=2) ⁶ S_(CO to C) _(n)

b) The CO₂-free selectivities of CO converted to detailed hydrocarbonsin liquid phase were calculated as:S _(CO to C) _(n) =A _(C) _(n) ^(FID2) ×f _(C) _(n) ^(FID2)/Σ_(n=5) ^(n)A _(C) _(n) ^(FID2) ×f _(C) _(n) ^(FID2) ×S _(CO to C) _(liquid phase)

Where A_(C) _(n) ^(FID2) is the off-line FID peak area of C_(n) (n>=5);f_(C) _(n) ^(FID2) is the correction factors of C_(n) (n>=5) 4 inoff-line FID.

Example 1

Dissolve 200.0 g of ferric nitrate nonahydrate and 5.92 g of manganesenitrate hexahydrate into 500 mL of deionized water, precipitate by using6 mol/L ammonia water as a precipitant at pH=8.0, age, filter, wash anddry at 120° C. for 12 h, and finally calcine at 500° C. for 5 h toobtain a precipitated FeMn catalyst having an iron-manganese atomicratio of 96 to 4.

Admix 5.0 g of the prepared FeMn catalyst into 50 mL of ethylorthosilicate solution, continuously stir, then perform rotaryevaporation to remove the solvent, dry and calcine to obtain a samplehaving a SiO₂ coating. Next, admix the sample into 50 mL of solutioncontaining tetrapropylammonium hydroxide template, ethyl orthosilicate,Al₂O₃, NaOH and H₂O in a ratio of 0.3:1.0:0.03:0.015:130, stir for 4 h,then charge into a hydrothermal kettle, seal, heat to 180° C., andhydrothermally crystallize for 48 h. Filter the solid product aftercrystallization and cooling, wash till the pH value of the washingliquid is 8, then dry at 120° C. for 12 h, and calcine at 500° C. for 5h to obtain a catalyst sample A with the weight percentage of a corelayer being 66%, the weight percentage of a transition layer being 9%and the weight percentage of a shell layer being 25%.

Example 2

Admix 5 g of the precipitated FeMn catalyst prepared in Example 1 into50 mL of aluminum isopropoxide trihydrate solution, continuously stir,then perform rotary evaporation to remove the solvent, dry and calcineto obtain a sample having an Al₂O₃ coating. Next, admix the sample into50 mL of solution containing tetrapropylammonium hydroxide template,ethyl orthosilicate, Al₂O₃, NaOH and H₂O in a ratio of0.3:1.0:0.03:0.015:130, stir for 4 h, then charge into a hydrothermalkettle, seal, heat to 180° C., and hydrothermally crystallize for 48 h.Filter the solid product after crystallization and cooling, wash tillthe pH value of the washing liquid is 8, then dry at 120° C. for 12 h,and calcine at 500° C. for 5 h to obtain a catalyst sample B with theweight percentage of a core layer being 64%, the weight percentage of atransition layer being 8% and the weight percentage of a shell layerbeing 28%.

Example 3

Take 5 g of 20 wt % Fe 1 wt % K/SiO₂ supported iron-based catalystprepared using an—incipient wetness impregnation method. Admix thesample into 50 mL of aluminum isopropoxide trihydrate solution,continuously stir, then perform rotary evaporation to remove thesolvent, dry and calcine to obtain an iron catalyst sample having anAl₂O₃ coating.

Next, admix the sample into 50 mL of solution containingtetrapropylammonium hydroxide template, ethyl orthosilicate, Al₂O₃, NaOHand H₂O in a ratio of 0.3:1.0:0.05:0.010:130, stir for 4 h, then chargeinto a hydrothermal kettle, seal, heat to 180° C., and hydrothermallycrystallize for 48 h. Filter the solid product after crystallization andcooling, wash till the pH value of the washing liquid is 8, then dry at120° C. for 12 h, and calcine at 500° C. for 5 h to obtain a catalystsample C with the weight percentage of a core layer being 74%, theweight percentage of a transition layer being 6% and the weightpercentage of a shell layer being 20%.

Example 4

Take 5 g of the catalyst sample A in Example 1, admix into 5.2 mL ofzinc nitrate solution by an incipient wetness impregnation method,perform rotary evaporation to dryness, dry at 120° C. for 12 h, andcalcine at 500° C. for 5 h to obtain a catalyst sample containing 3% ofmetallic Zn element by weight in the shell layer molecular sieve; next,admix the sample into an n-hexane solution containing 2 wt % of ethylorthosilicate, stir for 4 h, perform rotary evaporation to dryness, dryat 120° C. for 12 h, and calcine at 500° C. for 10 h to obtain acatalyst D.

Example 5

Take 2 g of the catalyst sample B in Example 2 to support a galliumnitrate solution by an ion exchange method, perform rotary evaporationto dryness, dry at 120° C. for 12 h, and calcine at 500° C. for 5 h toobtain a catalyst sample containing 2.5% of metallic Ga element byweight in the shell layer molecular sieve, next, admix the sample into15 mL of n-hexane solution containing 2 wt % of ethyl orthosilicate,stir for 4 h, perform rotary evaporation to dryness, dry at 120° C. for12 h, and calcine at 500° C. for 10 h to obtain a catalyst E.

Example 6

Take 2 g of the catalyst sample C in Example 3 to support a zinc nitratesolution by an ion exchange method, perform rotary evaporation todryness, dry at 120° C. for 12 h, and calcine at 500° C. for 5 h toobtain a catalyst sample F containing 4% of metallic Zn element byweight in the shell layer molecular sieve.

Examples 7˜11: Application of Invented Catalysts in Conversion ofSynthesis Gas to Aromatic Hydrocarbons

Mold the prepared catalyst under the pressure of 6.5 MPa, crush andsieve to obtain a sample of 40 to 60 meshes. Add 1.0 g of the catalystinto a continuous flow reactor, wherein the catalyst was pre-reducedwith one or more of hydrogen, carbon monoxide, methane, ethane andethylene gas for a certain period of time, and then cooled to thereaction temperature for continuous reaction. The reaction gas consistedof 45 vol % CO, 45 vol % H₂ and 4 vol % N₂, with N₂ as the internalstandard gas for calculating the conversion rate of CO. The product wasanalyzed on line under atmospheric pressure by a gas chromatographequipped with a thermal conductivity cell and a hydrogen ion flamedetector after cold trap, and the product in the cold trap was analyzedoff line by another gas chromatograph equipped with a hydrogen ion flamedetector.

Example 7

Put 1 g of the catalysts A to F into a pressurized fixed bed reactorrespectively, heat to 400° C. at 5° C./min in an H₂ atmosphere, andreduce under atmospheric pressure at the space velocity of 1000 h⁻¹ for10 h. Then, cool, introduce a reaction gas for reaction, andcontinuously react at the pressure of 1.0 MPa, the space velocity of5000 h⁻¹ and the temperature of 300° C. for 30 h, wherein the COconversion rate and the selectivity of each product were shown in Table1.

Example 8

Put 1 g of the catalyst D into a pressurized fixed bed reactor, heat to400° C. at 5° C./min in an H₂ atmosphere, and reduce under atmosphericpressure at the space velocity of 1000 h⁻¹ for 10 h. Then, cool,introduce a reaction gas for reaction, continuously react at thepressure of 1.0 MPa, the space velocity of 5000 h⁻¹ and the temperaturesof 250° C., 300° C., 350° C. and 400° C. for 30 h, and investigate theinfluence of the reaction temperatures. The CO conversion rate and theselectivity of each product were shown in Table 1.

Example 9

Put 1 g of the catalyst E into a pressurized fixed bed reactor, heat to400° C. at 5° C./min in an H₂ atmosphere, and reduce under atmosphericpressure at the space velocity of 1000 h⁻¹ for 10 h. Then, cool,introduce a reaction gas for reaction, continuously react at the spacevelocity of 5000 h⁻¹, the temperature of 300° C. and the pressures of0.5 MPa, 1.0 MPa, 2.0 MPa and 3.0 MPa for 30 h, and investigate theinfluence of the reaction pressures. The CO conversion rate and theselectivity of each product were shown in Table 1.

Example 10

Put 1 g of the catalyst D into a pressurized fluidized bed reactor and aslurry bed reactor respectively, heat to 400° C. at 5° C./min in an H₂atmosphere, and reduce under atmospheric pressure at the space velocityof 1000 h⁻¹ for 10 h. Then, cool, introduce a reaction gas for reaction,and continuously react at the pressure of 1.0 MPa, the space velocity of5000 h⁻¹ and the temperature of 300° C. for 30 h, wherein the COconversion rate and the selectivity of each product were shown inTable 1. The results were used for comparing the reaction results of thecatalyst in different reactors. The results showed that the results inthe slurry bed reactor and the fluidized bed reactor were similar, butboth are lower in the aromatic hydrocarbon selectivity than the fixedbed (Example 7).

Example 11

Put 1 g of the catalyst D into a pressurized fixed bed reactor, heat to400° C. at 5° C./min in an H₂ atmosphere, and reduce under atmosphericpressure at the space velocity of 1000 h⁻¹ for 10 h. Then, cool,introduce a reaction gas for reaction, and continuously react at thepressure of 1.0 MPa, the space velocity of 5000 h⁻¹ and the temperatureof 300° C. for 500 h. The CO conversion rate and the selectivity of eachproduct were shown in Table 1.

Comparative Example 1

Tablet, mold, crush and sieve the precipitated FeMn catalyst andFeK/SiO₂ catalyst prepared in Example 1 and Example 3 respectively, add1.0 g of respective catalyst of 40 to 60 meshes into a pressurized fixedbed reactor, heat to 400° C. at 5° C./min in an H₂ atmosphere, andreduce under atmospheric pressure at the space velocity of 1000 h⁻¹ for10 h. Then, cool, introduce a reaction gas for reaction, andcontinuously react at the temperature of 300° C., the pressure of 1.0MPa and the space velocity of 5000 h⁻¹ for 30 h, wherein the COconversion rate and the selectivity of each product were shown in Table2.

Comparative Example 2

Admix 5 g of the precipitated FeMn catalyst sample prepared in Example 1into 50 mL of solution containing tetrapropylammonium hydroxidetemplate, ethyl orthosilicate, Al₂O₃, NaOH and H₂O in a ratio of0.3:1.0:0.03:0.015:130, stir for 4 h, then charge into a hydrothermalkettle, seal, heat to 180° C., and hydrothermally crystallize for 48 h.Filter the solid product after crystallization and cooling, wash tillthe pH value of the washing liquid is 8, then dry at 120° C. for 12 h,and calcine at 500° C. for 5 h to obtain a catalyst sample G with theweight percentage of a core layer being 71% and the weight percentage ofa shell layer being 29%. Tablet, mold, crush and sieve the catalyst G,add 1.0 g of the catalyst of 40 to 60 meshes into a pressurized fixedbed reactor and a slurry bed reactor respectively, heat to 400° C. at 5°C./min in an H₂ atmosphere, and reduce under atmospheric pressure at thespace velocity of 1000 h⁻¹ for 10 h. Then, cool, introduce a reactiongas for reaction, and continuously react at the temperature of 300° C.,the pressure of 1.0 MPa and the space velocity of 5000 h⁻¹ for 30 h,wherein the CO conversion rate and the selectivity of each product wereshown in Table 2.

TABLE 1 Reaction performance of different catalysts for conversion ofsynthesis gas to aromatic hydrocarbons. CO Hydrocarbon productdistribution (CO₂-free C-mol %) Temperature Pressure/ conversion xyleneCatalyst ° C. MPa rate/% methane olefin alkane benzene toluene o- m- p-A₉₊ other A 300 1 63 15.4 0.3 15.3 10.6 21.5 3.9 1.2 28 2.3 1.5 B 300 159 14.5 0.4 14.2 11.7 22.4 3.5 1.7 27.5 2.1 2 C 300 1 38.2 15.8 0.4 15.29.9 18.8 3.1 2.1 30.1 2.2 2.4 D 300 1 69.4 13.5 0.4 10.5 13.5 18.2 4.61.3 32.5 3.6 1.9 E 300 1 67 11.2 0.6 7.5 14.8 20.7 4.3 2.6 34.5 2.6 1.2F 300 1 49.8 12.1 0.2 11.1 12.8 21.8 4.6 1.8 30.9 2.9 1.8 D 250 1 26.110.7 2.3 9.8 13.3 23.3 0.7 1.9 26.8 9.6 1.6 D 350 1 83 17 0.3 23.3 7.817.3 3.6 2.2 24.5 2.5 1.5 D 400 1 91 22.5 0.3 34.7 8.2 15.2 2.3 0.9 14.20.9 0.8 E 300 0.5 50 13 1.5 16 5.9 31.1 2.0 1.3 25.6 3 0.6 E 300 2 75.512.5 0.4 14.5 7.9 22.4 2.1 2.3 34.6 2.4 0.9 E 300 3 83 11 0.2 13 8.125.2 3.4 2.1 33.2 2.8 1 D 300 1 69.4 13.5 0.4 10.5 13.5 18.2 2.8 1.933.7 3.6 1.9 D* 300 1 56.5 15.5 1.2 12.5 8.8 18.2 3.5 0.6 27.1 8.2 4.4D** 300 1 58.1 16.3 1.6 11.8 9.5 18.8 4.2 1.1 24.6 8.1 4 D*** 300 1 6413.5 0.5 11 14.1 19.2 3.8 0.9 30.9 2.1 4 Reaction space velocity: 5000h⁻¹; average value of reacting 10 to 30 h. *, fluidized bed reactor; **,slurry bed reactor; ***, continuously reacting for 500 h.

TABLE 2 Comparative experiment results. CO Hydrocarbon productdistribution (CO₂-free C-mol %) Temperature Pressure/ conversion xyleneCatalyst ° C. MPa rate/% methane olefin alkane benzene toluene o- m- p-A₉₊ other FeMn 300 1 57.6 14.5 45.6 34.9 0 0 0 0 0 0 5   FeK/SiO₂ 300 135.1 20.1 48 29.6 0 0 0 0 0 0 2.3 G 300 1 60 13 1.2 15 6.9 18.3 7.2 5.110.2 18.9 4.2 G** 300 1 62 14.5 1.5 14.5 7.3 16.2 4.5 6.4 9.4 20.9 4.8Reaction space velocity: 5000 h⁻¹; average value of reacting 10 to 30 h.**, slurry bed reactor.

It can be seen from the comparison of the examples and the comparativeexamples in Tables 1 and 2 that the catalyst containing the transitionlayer oxide and with the molecular sieve layer being modified internallyand externally has higher selectivity to light aromatic hydrocarbons,the highest BTX selectivity is 76.9%, and particularly, the selectivityto xylene reaches 30% or above, accounting for 80 to 90% of the xylene.The catalysts with the molecular sieve layers not being modifiedinternally and externally show more heavy aromatic hydrocarbon products.

The disclosure described and claimed herein is not to be limited inscope by the specific aspects herein disclosed. Any person skilled inthe art can make modifications without departing from the spirit andscope of the disclosure. The scope of protection of the presentdisclosure should therefore be defined by the claims.

What is claimed is:
 1. A multistage nanoreactor catalyst, comprising astructure of a core layer, a shell layer and a core-shell transitionlayer; wherein the core layer is an iron-based catalyst havingFischer-Tropsch activity, a weight of the core layer being 0.1% to 80%of a total weight of the catalyst; wherein the shell layer is amolecular sieve, a weight of the shell layer being 0.1% to 80% of thetotal weight of the catalyst; and wherein the core-shell transitionlayer is a porous oxide or porous carbon material, a weight of thetransition layer being 0.01% to 35% of the total weight of the catalyst.2. The multistage nanoreactor catalyst according to claim 1, wherein theiron-based catalyst having Fischer-Tropsch activity is a supported orunsupported catalyst comprising additives.
 3. The multistage nanoreactorcatalyst according to claim 1, wherein the molecular sieve is one or amixture of two or more of ZSM-5, MCM-22, MCM-49, and SAPO-34 zeolitemolecular sieves.
 4. The multistage nanoreactor catalyst according toclaim 1, wherein the molecular sieve comprises additives.
 5. Themultistage nanoreactor catalyst according to claim 4, wherein an outersurface of the molecular sieve has a silicon-oxygen compound.
 6. Themultistage nanoreactor catalyst according to claim 4, wherein theadditives are selected from the group consisting of P, V, Cr, Mn, Fe,Co, Cu, Zn, Ga, Ge, Zr, Mo, Ru, Pd, Ag, W, Re and a combination thereof,and a weight of the additives is 0.01% to 35% of the weight of the shelllayer.
 7. The multistage nanoreactor catalyst according to claim 3,wherein the molecular sieve comprises additives.
 8. The multistagenanoreactor catalyst according to claim 1, wherein the molecular sieveis a zeolite molecular sieve, and silica-alumina ratio of the zeolitemolecular sieve is 10 to
 500. 9. The multistage nanoreactor catalystaccording to claim 1, wherein the porous oxide of the core-shelltransition layer is selected from the group consisting of silicon oxide,aluminum oxide, zirconium oxide, magnesium oxide, zinc oxide, titaniumoxide, calcium oxide and a combination thereof, and a thickness of thetransition layer is 0.1 to 1000 nm.
 10. The multistage nanoreactorcatalyst according to claim 1, wherein an outer surface of the molecularsieve has a silicon-oxygen compound, wherein a weight of thesilicon-oxygen compound is 0.01% to 20% of the weight of the shelllayer.